In semiconductor manufacturing apparatuses, general industrial machines and the like, conduit configurations including connection pipes are used for transporting fluids such as air, pure water, cooling water or hot water for temperature adjustment, organic chemical liquids, and the like. Such conduit configurations include a fitting structure for connecting a connection pipe to another member, for example, another connection pipe, or a fluid inlet/outlet of a housing of an apparatus.
Conventionally, as a fitting structure for connecting a pair of connection pipes to each other, for example, a configuration in which end faces of respective connection pipes are held in close contact with each other. In this event, an O-ring made of rubber is inserted between both end faces for enhancing the airtightness. Each end face is formed with a groove for holding the O-ring. In this regard, flanges may be formed in some cases on the end faces of the respective connection pipes, respectively.
In recent year, however, in semiconductor manufacturing apparatuses, for example, even a trace of impurities mixed in or even small fluctuations in pressure and in the flow rate of a fluid in a gas supply section which supplies gas to a reaction chamber, in particular, may result in manufacturing of defective products that cannot be used. Accordingly, airtightness at a significantly higher level than before is required for conduit configurations arranged in such positions. As mentioned above, the configuration including O-ring experiences difficulties in accomplishing a very high airtightness due to the nature of rubber which is the material of the O-ring, and reliability is more likely to degrade due to aging changes in the rubber. Further, no one can deny the possibility of modifications in characteristics caused by a chemical reaction of flowing gas and the rubber.
Thus, Japanese Patent Published Examined Application No. 62756/90 proposes a configuration for sandwiching a metal gasket, in place of an O-ring, between end faces of connection pipes (components of fitting). In this configuration, each end face is provided with an annular seal bead (protrusion), such that these seal beads are brought into contact with both sides of the gasket, respectively. In addition, the configuration employs a connecting nut which comprises a female thread in mesh with a male thread on the outer periphery of one connection pipe, and comprises an engagement section in engagement with the other connection pipe. By screwing the male thread of the connecting nut deep into the female thread of the connection pipe, the gasket is strongly pressed from both sides by the respective seal beads on both end faces to accomplish high airtightness.
Also, connection pipes made of metal such as stainless steel and a fitting structure made of metal such as stainless steel may be used in some cases. As a fitting structure made of metal, a double ferrule type fitting structure (see a catalog “(Gaugeable) Tube Fittings and Adapter Fittings” published in August 2004 by Swagelok Co.), or a single ferrule type fitting structure (see “CPI™ Tube Fittings catalog 4230 revised in February 2000” published in February 2000 by Parker Hannifin Corp.) has been used.
As shown in FIG. 1, the configuration described in the catalog of Swagelok Co., which is of a double ferrule type, comprises fitting body 44 having male thread 41 on the outer periphery and having insertion section 43 for metal connection pipe 42 in the inner periphery; nut 47 having female thread 46 in mesh with male thread 41 of fitting body 44; and front ferrule 45 and back ferrule 48 disposed within a space defined by the inner periphery of an end portion of fitting body 44 and the inner periphery of an end portion of nut 47. First engagement face 45a of front ferrule 45 is in engagement with cutout face 44a provided in the interior of the end portion of fitting body 44. First engagement face 48a of back ferrule 48 is in engagement with cutout face 47a provided in the interior of the end portion of nut 47. Then, second engagement face 45b of front ferrule 45 and second engagement face 48b of back ferrule 48 are in engagement with each other.
Accordingly, connection pipe 42 is inserted into insertion section 43 of fitting body 44, and male thread 41 is meshed with female thread 46 while nut 47 positioned on the outer periphery of connection pipe 42 is moved toward fitting body 44. In this event, as nut 47 moves toward fitting body 44, front ferrule 45 approaches back ferrule 48 such that they come into close contact with each other. Then, the end portion of second engagement surface 48b of back ferrule 48 is pressed onto and digs into the outer peripheral surface of connection pipe 42. In this way, connection pipe 42 is held by the end portion of back ferrule 48 that digs into the outer periphery of connection pipe 42.
Though not shown, the catalog of Parker Hannifin Corp. also discloses a fitting structure which includes a single ferrule which has an engagement face in engagement with a cutout face disposed in the interior of an end portion of a fitting body, and an engagement face in engagement with a cutout face disposed in the interior of the end portion of a nut, where the end portion of each engagement face is pressed onto and digs into the outer periphery of a connection pipe.
In this regard, in either configuration, either fitting body 44 or nut 47 is rotated while the other is fixed using, for example, two spanners or the like as tools so that male thread 41 of fitting body 44 is meshed with female thread 46 of nut 47.